Juniper IGP - CONFIGURATION GUIDE V11.1.X Configuration Manual page 213

# ICMP TooBigs Number of ICMP Too Big messages that the router has
received. When PMTU is disabled, this counter does not increase.
# ICMP TooBigs for unk. connection Number of ICMP Too Big messages
that the router has received for TCP connections that do not exist. When
PMTU is disabled, this counter does not increase.
PMTU Increase Attempts Number of attempts the router has made to
increase the PMTU
Black Hole Detect Threshold Number of successive transmissions that
must occur on a connection before that connection treats retransmissions
as indications that something is wrong
Override MSS MSS that is advertised to peers, overriding the MSS that
is derived from the interface MTU. This line does not appear in the output
if you do not set the value.
MTU/MSS information Information regarding path MTU/MSS
PMTU Status of MTU/MSS on this virtual router: enabled or disabled
MSS in effect MSS currently being used for transmission to the peer.
This number changes while various network events occur to cause the
router to increase or decrease its estimate of the MSS.
Calculated MSS to peer MSS that path MTU discovery has calculated
(if PMTUD is enabled) to the peer
MSS received from peer MSS that the peer received in a TCP MSS
option. If no option is received, the value is zero (0).
Application set MSS MSS that an application might have set for the
connection
Xmit Interface MSS MSS for the interface used to transmit packets to
the peer; calculated as the interface MTU minus the size of the TCP and
IP headers.
MSS Sent to Peer MSS that has been advertised to the peer
"ICMP DestUn, Frag Req'd and DF Set" messages Number of ICMP
"Destination Unreachable: Fragmentation Required and DF set" messages
that the router has received
Number of attempts to increase PMTU Number of times the router has
attempted to increase the PMTU by probing with a packet that is larger
than the known MTU
Time to next increase attempt Amount of time, in seconds, until the
router retries to increase the MTU
Black Hole Detection State State of the black hole detection mechanism:
none, detecting, probable, or unknown
Out-of-Order Packet Queue Information Information regarding packet
queue buffers
Chapter 2: Configuring IPv6
189
Monitoring IPv6